Mercury vapor rectifier



Aug. 16, .1932 I s, w|DMER 1,872,376

MERCURY VAPOR RECTIFIER Filed May 2a, 1928 2'Sheet sSheet 2' llllllllll Jwuenfop Patented Aug. 16, 1 932 UNITED STATES PATENT OFFICE swarm wrnmna, or BADEN, SWITZERLAND, nssrenon. mo renown, 30m: & cm, or

BADEN, SWITZERLAND, .A. CORPORATION 01 SWITZERLAND mnnc'omrivaroa 'nEc'rn-ma Application filed Kay 23, 1928, Serial No. 279,997, and in Germany June 11, 1927.

description of, exemplification thereof, refer ence being had to the accompanying draw- 10 ings, wherein Fig. 1. is a vertical sectional view through a metal tank rectifier embodying the invention' Fig. 2 is a vertical sectional View through 15 the anode and shield therefor. drawn in 're-' duced scale, illustrating in detail arrangement of my invention;

Fig. 3 is a horizontal sectional view through the shield arrangement along the lines IIIIII of Fig. 2;

Fig. 4: 1s a view simllar to trating a grid arrangement in which. the anode grid is insulated from the shield chamber enclosing the anode.

My invention, is of particular importance the grid in connection .with high power mercury arc' rectifiers of the metal tank type, although it is not necessarily limited 'thereto, and some of its features are useful and of importance in rectifiers of other types. In order to illustrate the invention, it will be described as applied to a rectifier of the metal tank type as shown in section in Fig. 1 of the drawings. It comprises a hermetically closed vessel including a main arc chamber 1 and a condensing chamber 2 on the top thereof. The are chamber is made of 'a" steel cylinder 3, the upper end of which is sealed by a massive anode plate 4 also of steel or similar mercury resistant material. 'At its lower end, the arc chamber cylinder 3 is closed by a bottom plate 5. The latter has in its middle an opening 6 which leads to the mercury container 7 formed of a short cylindrical body of insulating material such as porcelain that is closed at its bottom by a plate 8 of iron. A quantity of mercury 9 within this container serves as the cathode of the rectifier.

The anode plate 4 is likewise provided with a central opening over which is mounted the Fig. 2 illus-' condensing chamber 2 referred to above. This condensing chamber is formed of a main cylinder 11 that has its upper end closed. by

a metallic cover plate 11. In the center of this cover plate 12 is mounted the ignition coil 13 which operates the ignition electrode 14:to produce a current interrupting are at the surface of the mercury cathode and thus 7 re-entrant portion 'at the'lower end thereof.

The interior of the anode 15 may be hollow and is joined .to' a stem 16 extending through an insulating bushing 17 mounted within a suitable opening in the anode plate to insulatingly support the anode therein. The up- 3 per en of each anode stem is provided with a suitable heat-radiating member 18-for dissipating the heat' generated at the anode so as to maintain the same at a proper operating temperature. I

The anode chamber 3, the condensing chamber 2, and the cathode bottom plate 8 are likewise cooled by means of suitable jackets with cooling fluid such as water that is suitably circulated. An exhaust connection from an evacuating pump (not shown) is provided at 19 on the cover plate of the condensing chamber 2.

All the several arts of the rectifier structure as describeda ve are suitably joined to provide a hermetical enclosure and.the interior of the vessel is highly evacuated.

The cathode 9 is held insulated from the remainder of the body of the rectifier vessel and special insulated funnel members 21 and 22 are provided in the interior of the chamber to return condensed mercury so as to prevent formation of a continuous thread of mercury that might tend to establish an electrically conducting connection between the mercury cathode and any of the metallic wall.

portions of the rectifier vessel.

For the operation of rectifiers of this type,

I As seen in the drawings, the shields surrounding the anodes are made in the form of rela- .a forward current flow.

tively long tubular members of sheet metal. The anodes with the shields are disposed on the sides of the rectifier tank, the shields having openings at the bottom at a distance below the anodes and defining a substantial length of the arc path to the anodes. The shield openings are arrangedto lie outside the space above the cathode area so that the mercury blast from the cathode is prevented from entering into the shield.

As is well known, rectifiers of the foregoing type operate on the polyphase principle and each anode carries successively rectifying current during a portion of the rectifying cycle, this current flow being known as In the course of each alternating .current cycle, the individual anodes are successively substituted one for another, each carrying for a short period during which the respective anode is positive, forward current.

One of the drawbacks that the designers and operators of this type had to contend with in the past and which is particularly serious because of the large power and high voltages involved, was a tendency of such anodes to occasionally backfire or carry a re" verse current during the period when the anode became negative with respect to the oathode. Muchwork was done heretofore by the designers of such rectifiers and many attempts were made to find'a solution for this backfiring problem since the latter constitutes a very serious drawback and is one of the main reasons for the slow progress in adopting such rectifiers on a larger scale.

My invention is concerned with a new type of grid arrangement which greatly exceeds anything v to suppress backfiring in rectifiers of the type described above. V 1

Referring to the drawings, the grid of my invention may have the form of a series of concentrically disposed short sleeves 31,32, 33 of th'm sheet metal about one millimeter thick, located within the shield directly underneath theanode surface. The several cylinders 31-33, are held together by two stays 34, 35 disposed crosswise, one on the top and one on the bottom in short slots in the several cylinders and welded thereto so as to provide a substantially simple and relatively rigid body. By means of three 31" more spacing tubes 36 of metal, and bolts 37,- the grid is held fixed within the' anode shield in its appropriate place. The simple grid structure described above and arranged in the way shown in the drawings has a surprisingly strong effect in eliminating reverse. current proposed heretofore in-its ability very important to maintain the proper ratios;

and it is particularly important that the distances between the several parts be main tained in accordance with the figures given in the drawings. As seen from a comparison of the dimensions in Fig. 2, the effective length of the anode shield or sleeve 25, i.'e., the distance between the opening or mouth of the shield and the anode surface is relatively great compared with the distance of the grid from the anode and the length of the grid, although the latter extends over a substantialpart of the effective shield height. The entire grid is located in the upper third of the effective shield height, an the grid is higher than one-tenth of the effective shield height. The height of the grid is about five centimeters, and the distance between the grid and the anode surface is of the order of the'height of the-grid. However, departures from these figures given by me will likewise approach the desirable results obtained by my screen structure, and it is understood that Ido not wish to limit my invention altogether to grids having a particular set of dimensions. 1

One of the important features of the grid or screen structure is the fact that it is placed immediately adjacent the anode surface and that it is made entirely of metal. There is also they do not take up much space in a plane at right angles to the arc, and hence do not ad-' versely affect the operation of the forward are or rectifying current, or appreciably increase the voltage drop therein. I explain the beneficial effect of the-grids of my invention bythe fact that experiments and observations of the behavior of mercury vapor rectifiers have shown that as a general rule a backfire or reverse arc to an anode follows directly on the disappearance of the normal arc, that is'to say, the normal or forward current reverses practically instantaneously. It is known that the cause of the backfirev originates while the forward arc is operating and maybe due to an incandescent spot on the anode owing to non-uniform operation of thearc or to an incandescent foreign body of the anode. The cause of the backfire usually disappears as soon as the normal or forward arc is extinguished. Thus, the development of a backfire between the cathode or a normally operating anode andan anodewhich has for the time being assumed a negative potential may, it seems, be prevented by retarding the formation of the reverse are following the extinction of the forward arc, to an extent suflicient to enable the causes of the backfire to be removed before the reverse arc has been started. It would seem that this is among others accomplished by the grid or screen structure located and arranged in the path of the are as described above. It is understood. however, that I do not desire to limit m self to any particular theory of operation or unctioning of my improved rids, but I desire to embrace all the grid structures which embody the principle of those described by me.

edto a system in which a back electro-motiveforce exists, for instance, a system having in-. dependent sources of direct current connected thereto. In such systems, the rectifier must usually befirst connected through a resistance which may be cut out after the arc has been struck. out the use of a resistance if the grids are first given a positive striking charge from an auxiliary voltagesource. However, I have found that this is not always necessary and that under some conditions, it may be possible to operate rectifiers provided with such screens without any special paralleling resistance provided the rectifier has been initially treated so as to adapt the same'to such operation. v

The grid onscreen structures are, of course, made of a metal-which does not amalgamate' with ,mrcfir'y, for example, iron. \Vith heavycurrents, however, iron is liable to melt or become friable and therefore in some instances a more refractory metal 'such as tungsten may be preferable. As pointed out before, grids of the above description are .not

confined in their use to metal case rectifiers,

butare likewise suitable for other types of rec'tifiers, for instance, those of the glass-bulb type. The invention is likewise not limited to grids using circular tube sections, but similar beneficial-effects will be obtained with structures using other sections, for instance,

checkered or corrugated tubular forms.

In some cases, it may be desirable to insulate the grid from theshield structure itself,

such arrangement being shown in Fig. 4 in which the spacing tubes 41 betweenthe screen and the shield are made of an insulating material, such as porcelain and the bolts .42 con- The rectifier may be paralleled with-- necting the screen to the shield are likewise insulated from the shield by interposing suitable insnlating washer 43. The advantage of mounting the grid in such a way: lies in the possibility ofiered thereby of electrically interconnecting the grids of several anodes in the rectifier. 'Such arrangement furthermore permits giving the grids a positive striking or negative extinguishing potential with respect to the corresponding anode, or more generally, it permits-independent control of the potentialof the grids in case this is desired. Y

My invention is not limited to the particular details or features of construction, or the-- .ory of operation pointed out above, and I de-' sire accordingly, that the appended claims be given a broad construction commensurate with the scope of the invention within the art.

I claim: 1 In a vapor discharge device, an anode. --having,an' active surface and a grid positioned at a shortdistancein front of said surface comprising sheet metal members sub- 1' dividing the space in front of said active anode surface 1nto a plurality of channels leading in the direction of the arc, the material formingsaid channels occupying .a relatively negligible. portion of the space ma direction transverse to the arc and leaving the space between said members unob 'structed, the length ofsaid channels being approximately of the order of the distance between said grid and said active anode surface. V p A .2. In'a vapor discharge device, an anode,

and-a grid placed-in the path of the are to said anode, said grid comprising a plurality of concentrically arranged'tubular members sub-dividing-thearc space into a plu rality of parallel arc channels leading to the anode.

3. In a vapor dischar gedevice, an anode,

a vaporizable cathode remote from said anode, a sleeve surrounding said anode and defining an arc path towardssaid cathode,

said sleeve having an opening for said are path at a distance from said anode and a grid across said are path located within sald sleeve nearer-to said anode than to said opening, said grid constituting a plurallty of longitudinal channels extending the direction of the arc path.

4. In a vapor discharge device, an anode, a vaporizable cathode remote from said anode,

.a metallic sleeve surrounding said anode and defining an arc path towardssaid cathode,

said metallic sleeve having an unobstructed opening for said arc path ata distance from said anode, and a metallic gridacross said are path located within said sleeve nearerto said anode than to said opening, said grid constituting a plurality of longitudinal channels extending in the direction of-the arc path.

5. In a vapor discharge device, an anode, a cathode, a metallic sleeve surrounding said anode and defining an arc path towards said cathode, said sleeve having an opening for said are path at a. point relatively remote from the active anode surface, and a metallic grid disposed in said sleeve in the direc tion transverse to said are path, said grid being located at a'point in said shield nearer tosaid active anode surface than to said sleeve opening, said grid being formed of sheet metal portions constituting longitudinal channels in the direction of the arc path, said grid occupying a substantial length in the, direction of saidarc path and a substantially negligible area in the direction transverse thereto, leaving the space between said metal portions substantially unobstructed.

6. In a mercury vapordischarge device, an anode, a mercury cathode remote from said anode, a tubular metallic sleeve surrounding said anode and extending for a distance therefrom to define the arc path to said cathode, said sleeve having a substantially unobstructed arc-admitting opening at a. distance from said anode,'and a-metallic grid disposed insaid'sle'eve transversely to the are at a distance equal or less than onethird of the distance between said anode and said opening, said g'rid' constituting a plurality of longitudinal channels extending 1n the direction of the arc path. 1

7 In a vapor discharge device, an anode, a mercury cathode removed from said anode, a tubular -metallic sleeve surrounding said anode and extending for a substantial length therefrom to define an arc path, an opening in said sleeve at a distancefrom said anode, and a metallic grid disposed within said sleeve transversely to the arc path, said grid comprising thin sheet metal members ex tending in the direction of the arc pathto constitute a plurality. of parallel arc channels, the distance between said grid and said anode surface being less than one-third. of the distance between said anode surface and said shield opening, and the length of said channels being of the order of the distance between said grid and said anode.

8. In a vapor discharge device, a gas vessel containing a vapor, a cathode, an anode for maintaining a discharge with said cathode through said vapor, an insulated sleeve around said anode having an opening at a distance therefrom and confining a substantial length of the discharge path between said anode and said cathode, and sheet members subdividing asubstantial length of said sleeve in front of said anode into longitudinal chan nels extending in the direction of the discharge toward said anode, said sheet members being of small thiclmess and occupying a substantially negligible area in the direction transverse to the discharge, leaving the space tight between saidsheet members free for the pas sage of the discharge. a

9. In a vapor discharge device, a gastight vessel containing a vapor, a cathode, an anode for maintaining a discharge with said cathode through said vapor, an insulated sleeve around said anode having an opening at a. distance therefrom and confining a substantial length of the discharge path between said anode and said cathode, and sheet members subdividing a substantial length of said sleeve in front of said anode into longitudinal channels extending in the direction of the discharge toward said anode, said sheet members being of small thickness and occupying a substantially negligible areain the direction. transverse to the discharge, leaving the space between said sheet members free for the passage of the discharge, the length of said channels being not more than twice the small- .est width of said channels. I

'10. In a vapor discharge device, a gas tight vesselcontaining a vapor, a. cathode, an anode for maintaining a discharge with said cathode through said vapor, an insulated sleeve around said anode having an opening at a distance therefrom and confining a substantial length of the discharge path between said anode and said cathode, and metallic.

. said sheet members being of small thickness and occupying a substantially negligible area in the direction transverse 'to the discharge,

leaving the space between said sheet members free for the passage of the discharge;

- 11. In, a vapor discharge device, a gas tight vessel containing a vapor, a cathode, an anode for maintaining a discharge with said cathode through said vapor, an insulated sleeve around said anode having an opening at a distance therefrom and confining a substantial length of the discharge path between said anode and said cathode, and a grid formed of metallic sheet members subdividing a substantial length of said sleeve in front of said anode into longitudinal channels extending in the direction of the discharge toward said anode, said sheet members being of small thickness and occupying a substantially negligible area in the direction transverse to the discharge, leaving the space between said sheet members free for the passage of the discharge, said grid being nearer to the anode than to said-sleeve opening.

- 12.- In a vapor discharge device, a gas tight vessel containing a vapor, a cathode, an anode for maintaining a discharge with said. cathode through said vapor, an insulated sleeve around said anode having an opening at a distance therefrom and confinin a sub- .stantial length of the discharge path said anode and said cathode, and a grid tween v sleeve around said anode confining a portion passage of the discharge.

formed of metallic sheet members subdividing a substantial length of said sleeve in front of said anode into longitudinal channels extending in the direction of the discharge toward said anode, said sheet members being of small thickness and occupying a substantially negligible area in the direction trans verse to the discharge, leaving the space between said sheet members free for the passage of the discharge, said grid being within 10 centimeters from said anode.

13. In a vapor discharge device, a gas tight vessel containing a vapor, a cathode, an anode for maintaining a discharge with said cathode through said Vapor, an insulated of the length of the discharge path extending from said anode to the cathode, andconduct ing partition members carried by said sleeve at a distance in front of said anode-andsubdividing the cross-sectional area of said confined discharge path into a plurality of lon-"" gitudinal channels extending parallel to each other in the direction of the discharge, the transverse area occupied by said partition members occupying less than about one-fifth of the cross-sectional area of said channels,

the length of said channels being of the order of their distance from said anode.

14. In a vapor discharging device, a gas tight vessel containing a vapor, a cathode, an anodefor maintaining'a discharge with said cathode through said vapor, an insulated sleeve around said anodehaving an opening at a distance therefrom and confining a portion of the discharge path between said anode and said cathode, and partition members supported by said sleeve in front of said anode and subdividing said discharge path into lon gitudinal channels extending in the direction of the discharge toward said anode, said partition members occupying a transverse area small compared with the cross section tion of the discharge toward said anode, said partition members occupying a transverse area small compared with the transverse area of said channels, leavin the space between said partition members Iree for thepassage of the discharge.

17. In a vapor discharge device, a gas tight vessel containing a vapor, a cathode, an anode for maintaining a discharge with said cathode through said vapor, an insulated sleeve around said anode having an opening at a distance therefrom and confining a portion of the discharge path between said anode and said cathode, and a grid formed of metallic partition members supported by said sleeve in front of said anode and subdividing said discharge path into longitudinal channels extending in the direction of the discharge toward said anode, said partition members occupying a transverse area small compared with the transverse area of said channels,

anode.- s

In testimony whereof I have hereunto subscribed my name. STEFAN WIDMER.

a1 area of the channels, leaving the space between said partition members free forthe 15. In a vapor discharge device tight vessel containing a vapor, a cathode,an anode for maintaining a discharge with said cathode through .said vapor, an insulatedsleeve around said anode having an opening at a distance therefrom and confining a portion of the discharge path between said anode and said cathode, and partition members supported by said sleeve in frontof said anode and subdividing said discharge path; into longitudinal channels extending in the direction of the discharge toward said anode, said partition members being of small thiclmess and occupying inthe direction transverse to the discharge a small area compared to the area of said channels, leaving the space between said partition members free for the passage of the discharge, the length of said a gas 

